lunes, 13 de junio de 2011

GSoC2011: Unification of X11 code and wsys device

The main objective of this project is to reduce the duplication of code between the different Plan 9-like drawing devices which run on X11. Currently, there are four similar (but subtly different) implementations. Charles Forsyth (mentor of this project) made a very clear explanation of which is the current situation, I've taken the freedom to reproduce it here:
  1. The existing devdraw program runs on x11 and osx. It implements the plan 9 graphics protocol, but embeds that in a novel non-9p protocol. Only p9p's programs can talk to it, through a modified libdraw.
  2. Inferno and plan 9 use the original libdraw (more or less) to access draw's primitives through a name space that's implemented by draw(3), a kernel driver. draw(3) uses libmemdraw for graphics. Applications access the name space by binding a local device or mounting a remote 9p connection.
    1. Plan 9's kernel driver port/devdraw.c gets */screen.c to do the work, typically in flushmemscreen (or hwdraw). 
    2. Inferno's kernel driver uses x11, osx, windows and native variants of win.c or screen.c (roughly speaking), with most of the work done in attachscreen and flushmemscreen.
  3. Drawterm and 9vx implement draw(3), drawing using a libmemdraw that devolves a lot of the work to special x11 and osx variants, and using a few geometry primitives from libdraw. 9vx applications are just plan 9 applications, and they use plan 9's libdraw.
Except for minor differences that can get in the way in practice, Inferno, Plan 9, and 9vx can all draw on each other's screens. They can also all draw on a drawterm screen (again, if not prevented from doing that by minor differences).
Inferno and drawterm are the only ones that run on Windows. The others, except for Plan 9, run on Unix-y systems like Linux, and on MacOSX.
Only p9p programs can talk to the devdraw program directly, and (I think this is right) they can't talk to any of the other systems directly. Generally, p9p is the odd one out. On the other hand, p9p uses a separate program to do the graphics, and that has advantages in hosted environments.
In order to improve this state of things, a new wsys device will be written. This device will be a unix program which uses xlib and serves 9p. Being a 9p server, it will be possible to mount it from Inferno, 9vx and drawterm without any modificaions. It is still to be decided how the new device will be used from p9p.

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